Titel: Higher-Order Closure Meso-Scale Modellling For Wind Climate Estimates
Författare: Hans Bergström
Utgivare: Uppsala Universitet
Årtal: 2003
Ämnesord: Vindmeteorologi
Sökord/keywords: meso-scale model, meteorologi, MIUU.
Rapport (Pdf)
Sammanfattning/Abstract: The use of meso-scale models for wind resource assessments has increased during resent years. Especially in complex terrain, the need for more advanced models than has earlier been used is often obvious. Also observations of offshore winds over the Baltic Sea show complexity and in-homogeneity to a much larger extent than are often expected regarding offshore winds.
Results with a higher-order closure meso-scale model, (the MIUU-model developed at the Department of Meteorology, Uppsala University), show that with this type of model the observed complex and inhomogeneous wind fields also turn up in the model results. A higher-order closure model is, however, computer-time consuming to run, why care has to be taken to limit the number of model runs needed as much as possible.
A method to simulate the climatological wind field using the MIUU model has been developed at Uppsala University, reducing the total number of simulations needed. With this method a limited number of climatologically relevant simulations are performed, with different wind and temperature conditions, and a weighting based on climatological data for the geostrophic wind (horizontal pressure gradient) is made in order to finally estimate the wind climate. The method is applicable for mapping the wind resources with a resolution of 0.5-10 km. To use this method geostrophic wind (strength and direction), sea and land temperatures, topography, roughness, and land use are needed. No observed boundary-layer winds are needed other than for verification. Comparisons between model results and measurements show good agreement.
As it is desirable to minimize the number of model runs, it is important to optimise the choice as regards how the climatologically most relevant parameters are varied. How this should be done is, however, not obvious. The sensitivity of the resulting wind climate to this choice is therefore tested, using a large number of different combinations of the parameters being of importance. Among the factors investigated, and how they influence the wind climate, are: a) annual variations of land- and sea surface temperatures, b) magnitude of the geostrophic wind, c) direction of the geostrophic wind, d) importance of the temperature- and humidity profiles, representing different air masses, and which are used to initialise the model, e) importance of the thermal wind – i.e. variations with heights of the gesotrophic wind.